I have a Focus EV and a model S. The Focus uses a permanent magnet motor and thus can regenerate to a full stop. The Tesla uses an induction motor. Basically at very low speeds, it is not able to generate the magnetic field necessary to fully engine brake.
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johnr
Member
I had a 2011 Leaf, and the braking behavior was very unpredictable. The braking force fluctuated from one time to the next, and in stop-and-go driving it would grab. It was a source of never-ending frustration. That thing was a lemon.
I promptly traded it for a 2014 iMiev the first chance I got. The iMiev does have consistent braking behavior, with the exception of tight turns and rough roads which would temporarily cut regen (the Leaf also had that problem).
My current car, a 2013 Model S, I find has perfectly consistent regen which never falters even on the worst of roads. The increase in regen at lower speeds compensates for the reduced wind resistance at slower speeds, resulting in a fairly linear deceleration. The only time frictions brakes are needed is to come to a complete stop, and for panic braking. During a test drive of a 2016 model it seemed about the same. In my opinion their implementation of regen was quite well thought out in its simplicity and execution. Just my 2 cents
The OP may wish to visit a service center and have them check it. That graph does look kinda weird.
I promptly traded it for a 2014 iMiev the first chance I got. The iMiev does have consistent braking behavior, with the exception of tight turns and rough roads which would temporarily cut regen (the Leaf also had that problem).
My current car, a 2013 Model S, I find has perfectly consistent regen which never falters even on the worst of roads. The increase in regen at lower speeds compensates for the reduced wind resistance at slower speeds, resulting in a fairly linear deceleration. The only time frictions brakes are needed is to come to a complete stop, and for panic braking. During a test drive of a 2016 model it seemed about the same. In my opinion their implementation of regen was quite well thought out in its simplicity and execution. Just my 2 cents
The OP may wish to visit a service center and have them check it. That graph does look kinda weird.
This was taken when regen was limited to around 1/4 of its full power. Actual for cold climates. That is unexpected behavior and few other owners confirmed they experience the same.
Later I logged regen deceleration curve with warm battery and 100% power available and it works fine (like it should, almost linearly).
So my conclusion is - most probably it is design flaw due to lack of testing/engineers attention to the cold climate performance.
I've added to the chart power returned to the battery. Interestingly enough it is modulated in wide range in order to produce nearly linear acceleration. So in fact Tesla tried good enough to make regen braking consistent. Algorithm flawed for cold battery only. Otherwise I'm satisfied.
legoman
Member
Great chart, but it seems like not a real-world driving test. How many times in daily driving can you decelerate from 75mph to 0mph in 34 seconds with no other factors (no other cars in the area, no change in elevation, etc.)? I think your first chart is more realistic to what people experience.
I also wonder if there is some regen program logic that tries to guess if you are speed-adjusting with no intention of stopping (e.g. traffic ahead (non TACC), change in speed limit, etc.) vs. coming to a complete stop. It's probably my butt-dymo, as you put it, but it feels like the regen behaves a little differently when you are intending to come to a complete stop.
I also wonder if there is some regen program logic that tries to guess if you are speed-adjusting with no intention of stopping (e.g. traffic ahead (non TACC), change in speed limit, etc.) vs. coming to a complete stop. It's probably my butt-dymo, as you put it, but it feels like the regen behaves a little differently when you are intending to come to a complete stop.
My guess is that car engage full regen only if you lifted up your feet from accelerator completely after some delay (~1 sec) by my measurement.
See below (after fully depressing accelerator I lifted my feet from it completely as fast as I can).
Notice there is ~1s delay between full power draw and full regen.
I didn't feel any difference in regen when other cars are present versus empy road.
See below (after fully depressing accelerator I lifted my feet from it completely as fast as I can).
Notice there is ~1s delay between full power draw and full regen.
I didn't feel any difference in regen when other cars are present versus empy road.
stopcrazypp
Well-Known Member
I don't think a PM motor will solve the problem. The problem is at extremely low speeds, the efficiency . This affects PM motors too, since although it doesn't have the overhead of generating the magnetic field, it still has the resistive losses.
So to get a consistent and useful amount of braking power down to a stop even a PM motor would have to consume power to brake to a stop. This may or may not match a definition of "regenerative braking" (although in practical terms, if you assign a braking ).
Reference here done using PM motors that show certain torque/speed regions where regen braking can't occur on page 48:
https://smartech.gatech.edu/bitstream/handle/1853/47660/sambamurthy_aravind_201305_mast.pdf
stopcrazypp
Well-Known Member
I didn't realize that my draft was what was posted, instead of the final, but here is it edited:
I don't think a PM motor will solve the problem. The problem is at extremely low speeds, the efficiency drops drastically and maximum braking torque it can provide goes down. This affects PM motors too, since although it doesn't have the overhead of generating the magnetic field, it still has the resistive losses.
So to get a consistent and useful amount of braking power down to a stop even a PM motor would have to consume power to brake to a stop. This may or may not match a definition of "regenerative braking" (although in practical terms, you can assign a constant brake torque and use power or mechanical brakes to simulate the feeling, although it won't generate any energy).
Reference here done using PM motors that show certain torque/speed regions where regen braking can't occur on page 48 (the blue line shows maximum negative torque it can provide with regenerative braking):
https://smartech.gatech.edu/bitstream/handle/1853/47660/sambamurthy_aravind_201305_mast.pdf
johnr
Member
Glad to hear that. True, the regen is limited when the battery is cold - and I'm not surprised the deceleration profile is affected as a result.
Here are some ideas I've found from various places (as I don't have any personal experience with cold weather) - some might help, and some might not: Leave the car plugged in as much as possible; schedule it to stop charging shortly before you leave in the morning; turn off "range mode"; preheat the car before leaving; keep it in a warm garage; charge to no more than 70-80%.
Thanks for the ideas. It looks like trading one inconvenience to another. I plug my car once a week (85%-30% charge drop during the work week). I will rather keep it that way. My garage is not warm unfortunately. I tried to turn range mode off - not much difference. It is not enough time to warm battery up on my 10mi commute.
Anyway it is spring and summer is coming
Anyway it is spring and summer is coming
green1
Active Member
Unrelated to this thread, but why not plug it in every day if you park in a garage anyway? It's better for the battery to frequently charge small amounts than to infrequently charge large amounts. There are also the added benefits of reduced likelihood that you'll forget to plug it in on "charge day", and that it will always be ready for an unexpected trip.Thanks for the ideas. It looks like trading one inconvenience to another. I plug my car once a week (85%-30% charge drop during the work week). I will rather keep it that way. My garage is not warm unfortunately. I tried to turn range mode off - not much difference. It is not enough time to warm battery up on my 10mi commute.
Anyway it is spring and summer is coming
It is not better to charge everyday to 85% than to have it float around 50% for several days.
green1
Active Member
Proof? Tesla recommends leaving it at 90%, but has allowed people to chose lower (though not below 50 as they know that's likely to decrease longevity)
Additionally, my claim was not in regards to choosing a specific level, but in relation to wide swings vs narrow swings.
If all you ever need is 10% of the pack a day, and want to use the 10% between 60 and 50, that's your choice, but you'd still be better off charging every night then charging to 90, waiting 6 days for it to get down to 30 and then charging back to 90.
There are several studies on the subject. The lower you keep the charge the better, until you get too low, at which point you start doing damage.
Lithium Battery Failures
Never seen any data showing this. Don't know why it could even be true, given the data above.
edit: and your BMS will get completely decalibrated if you only keep the car in a narrow range.
green1
Active Member
Your "study" doesn't even talk about the topic I mentioned... all it says is to keep it between 20-90% (and nothing about the "the lower the better" that you just asserted. However if you really do believe that lower is better, you'd want to charge a small amount frequently. If you charge every night to 50 and let it drop to 40 during the day and charge it up to 50 again, you never get to 80 or 90, but if you charge to 90 and let it drop to 40, you spend most of your time with a charge state above 50. So your own logic says to charge small amounts frequently.)
What your "study" does state is that any excursion outside of the operating window has damaging effects. So based on that alone, we know that you're better to keep it charged higher rather than lower to avoid dropping too low if you suddenly have to drive further than you expected, or in colder weather, or sit longer, or any of a number of other things.
There have been many studies on "cycles" of a battery, and they all agree that fewer larger cycles are always more damaging than many smaller cycles (assuming the same amount of total charging is done). This isn't your old NiCd, there's no "memory effect".
Because I have only one bay with charger in my garage and it is usually taken by my second electric car that needs to be charged everyday. So it is definitely a hassle to shuffle cars every day/night/morning to just top my Tesla's battery if I don't have to.
Not worth the inconvenience.
It clearly has more data than that, and I'm not about to include the dozen others that also have that data.
I believe you're misreading the results of those studies, the key factor here being that smaller cycle done near 50% is better than than same energy going through 0% and 100%.
green1
Active Member
Most people find it far more convenient to plug in every night so they never forget, AND it's better for the battery to boot, win-win.
No, you completely misunderstand. charging from 50-60% daily is ALWAYS better for the car than charging from 20-90% weekly (or 40-70 every 3 days.)
It doesn't matter if you claim it's because the maximum charge level is lower, or because the total swing is less, either way it's better. So based on your own argument that the lower the charge state the better, it would be best to charge nightly (or more if possible) even if you think that I, and every battery scientist, and Tesla themselves, are wrong about it being better, your own argument agrees!
I'm not plugging in everyday. Period. Given that, it's best to go through a range of SoC. Not to mention, you completely ignored the BMS calibration issue. Good luck taking a long trip if your car has only seen a 10% range of SoC for months at a time.
green1
Active Member
Hasn't affected any of my long trips. if it affects yours, maybe you should have it looked at.
If you don't want to plug in every day, that's your choice.
I'm just saying that it's one that is not based in what's best for the battery.
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